This invention was made with Government support under U.S. Army Grant No. DAAD05-86-M-3777 awarded by the Department of the Army. The Government has certain rights in this invention.
This invention relates to heavy metal alloy systems and, in particular, to such systems in which strength and hardness is increased through molybdenum additions while retaining a moderate level of ductility. A process for making such alloy products is also disclosed.
In this application, reference to "classic tungsten heavy alloy system" shall mean the alloy composed nominally of 90% by weight of tungsten as its major constituent and nickel and iron in the ratio of 7:3 as its minor constituent.
Tungsten heavy alloys have attractive property combinations of relatively high density, high strength, high ductility and easy machinability. As a result, this class of alloys is very useful for numerous applications like radiation shields, counterbalances, heavy duty electrical contacts, vibration dampers and, to some extent, kinetic energy penetrators. However, their usefulness, particularly as kinetic energy penetrators, can be enhanced if their strength and hardness can be made even higher while retaining moderate ductility, say 1 or 2%, and a reasonably high density, say 15 g/cc or above. There has been some attempt to improve the strength of these alloys by alloying additions like cobalt, chromium, rhenium, platinum, titanium, small amounts of molybdenum and aluminum, but they have not been very successful. Typically, the ductility of the alloys is significantly lowered by these additions which tend to form embrittling intermetallic phases.
Also, in the past, there has been relatively little effort to increase the hardness of heavy alloys through alloying. Until now kinetic energy penetrators, especially those used for piercing heavy armor plates, have been made with depleted uranium as an important constituent. This material is, of course, both toxic and expensive. It would, therefore, be highly desirable if a new material could be found which has the necessary mechanical properties, which is relatively inexpensive and which does not pose a hazard to health or require special handling procedures.